The present invention relates to resistive wire mass flow meters.
In his French patent application FR-2.728.071, the applicant has already proposed a hot wire flow meter for measuring a mass flow.
In it current pulses are sent through the resistive wire during given periods and the cooling speed of the wire between the pulses is measured.
It has been observed that such hot wire measuring sensors could exhibit a drift over time because, in particular, particles of grease can become deposited on the resistive wire, thus falsifying the thermal behavior of the latter.
One purpose of the invention is to propose a mass flow meter comprising means allowing this drift to be detected.
Another purpose of the invention is to propose a mass flow meter comprising means making it possible to detect operational anomalies of the electronics associated with said flow meter.
From U.S. Pat. No. 4,335,605, it is known to compare measured values with threshold values in order to detect possible operational anomalies of a flow meter.
Such processing is not very effective and does not make it possible to determine a possible drift or possible anomalies sufficiently early.
Neither does it allow a determination making it possible to correct possible drifts or anomalies.
The invention however proposes a mass flow meter of the type comprising a heating probe placed in the path of a fluid whose flow rate is to be measured, means of applying current pulses to said probe, measuring means for determining its cooling speed between said pulses, characterized in that it comprises processing means capable of determining a characteristic parameter of at least a portion of a cooling curve of the fluid and for deriving from that parameter data relating to a possible operational drift or anomaly.
Advantageously, the processing means determine the parameter after the generation of a current pulse in the absence of flow of fluid and comprise means of generating such a pulse when a start of a phase of utilizing the flow meter is detected and before the flow of the fluid is established.
According to a particularly advantageous embodiment, the processing means comprise means of determining a characteristic parameter of a first cooling phase during which the heating probe is cooled by conduction through the material which forms it and through its cover and possible oily, greasy or solid deposits, said processing means also comprising means of deriving from this parameter data relating to a possible drift due to said oily, greasy or solid deposits.
Also, the processing means can comprise means of determining a characteristic parameter of a second cooling phase during which the heating probe is cooled, also by conduction, in the fluid, but at a zero fluid flow rate and not by convection, as well as means for deriving from this parameter data relating to a possible operational anomaly of the electronics of said flow meter.
Other characteristics and advantages of the invention will furthermore emerge from the following description.